1. Field of the Industrial Application
The present invention relates to a compact printing apparatus such as a time recorder and a time stamper, and more particularly to a printing apparatus for printing information on pieces of printing paper having various thicknesses, which paper is manually inserted into the apparatus.
2. Prior Art
For instance, as one of such printing apparatus, there is provided a serial type printing apparatus. In order to obtain a high quality print, during the printing operation, it is necessary to keep a gap between a printing head and a printing surface of paper at a level 1 mm or less. Also, it is necessary to keep the gap constant even for pieces of paper having various thicknesses.
In view of the fact that the sheet such as a time card or the like is manually inserted, it is important that the insertion of the printing paper is easy and the sheet is fixed so as not to be displaced in position.
To meet this requirement, as shown in, for example, Japanese Patent Application Laid-Open No. Hei 4-50253, a frame plate on which is mounted a mechanical portion including a printing head, a guide shaft and the like is mounted to be movable relative to a base frame in a direction of the thickness of the printing paper, a spring is provided for always drawing the frame plate toward the base frame, and a cam disc is provided on a cam shaft for moving the printing head in the printing direction, for moving the frame plate upwardly against the drawing force of the spring to thereby expand the passage, into which the printing paper is to be inserted when the printing head is moved toward the printing start position and for moving the frame plate downwardly toward the base frame by releasing the force for moving the flame plate upwardly during the printing operation. Also, a rubber stopper is provided on the frame plate so that the gap between the printing head and the printing paper surface is kept constant and the printing paper is retained in place.
In such a conventional apparatus, since the printing mechanical portion including the printing head as a whole is moved, a structure for moving the printing mechanical portion as a whole is complicated, and its assembling property is degraded. Also, since the portion which moves is heavy in weight, it is difficult to increase the speed of the operation and a motor having a high output power for moving the portion is needed. Furthermore, since the high precision mechanical portion including the printing head is moved, the manufacture cost is increased and the printing quality is degraded.
In view of these defects inherent to the conventional apparatus, an object of the present invention is to provide a printing apparatus in which a mechanical portion that is heavy in weight and needs a high precision is simplified in structure, thereby increasing the printing operation and ensuring a stable printing quality in low cost.